Continuous counter current extractor



Nov. 19, 1963 J. c. CAVANAGH ETAL CONTINUOUS COUNTER CURRENT EXTRACTOR Filed Sept. 1. 1960 2 Sheets-Sheet 1 AVA A ll 4AA AVIL I8 7 19 9 o o o o I o o o o o o 02 0 o 0 24a,- 16 A E E Egg 2. INVENTOR ATTO RNEYS 1953 J. c. CAVANAGH ETAL 3,111,393

CONTINUOUS COUNTER CURRENT EXTRACTOR Filed Sept 1. 1960 2 Sheets-Sheet 2 9 6 INVENTOR J'OH CH RLES AV NAGH RTTORNHYS 3,lll,393 CONTENUUUS {IGUN'EE CURRENT EXTRAQTOR .io:.n harles Cavanagh, 3.58 Arleiaide Terrace, Perth,

Western Australia, Australia, assignor of one-half to Edwin George human, lerth, Western Australia, Aestralia Filed ept. l, 196% Bar. No. 53,3??- Qlaims priority, application Australia Eiept. 3, E59 4 Claims. (5. iii-Q69) This invention relates to an improved continuous counter current extractor for the treatment of solid particulate material with a liquid in counter current flow.

One object of the invention is to provide a continuous counter current extractor which is relatively simple and economical in construction and operation, has a high throughput in relation to size and which has a wide range of application.

Another object of the invention is to provide an extractor which is readily adaptable to operation with a volatile solvent under sealed conditions and which is particularly suitable when the solid material being extracted is of a porous or spongy nature and has a strong tendency to occlude the extraction liquor and when the outgoing extraction liquor is very viscous or contains a liquid fat or oil in a separate phase or in globule or emulsion form.

Broadly, the invention resides in a continuous counter current extractor comprising a plurality of stages, each stage comprising a container for a body of liquid, means for agitating solid particulate material in the body of liquid, and means for substantially separating the solid particulate material from the liquid and feeding the substan tially separated solid material to the next stage whilst, simultaneously, the liquid passes back into the previous stage.

Preferably, the separating and feeding means comprise a type of screw press.

The press contains a compression screw operating inside a shell which is wholly or partly perforated or slotted A to allow of squeezing of the Solid material and expression of the liquid. Preferably the flights of the screw scrape evenly over the surface of the shell or close to it in order to prevent build up of solid material which might block the perforations or slots. The screw and shell may be extended backwards into the region Where the agitated mixture of solid and liquid is fed in so that, if the mixture is thin or sloppy, sufiicient liquid drains off in this region to provide a cake or sufficiently compacted solid material to be picked up by and drawn into the compression part of the screw. These two regions may be referred to as the drainage zone and the expression zone. This combination of screw with drainage and expression zones fulfills two functions in that it provides an efiicient separation of drained and expressed liquid in relation to liquid remaining with the solid and it also performs the mechanical function of automatically propelling the solid material from the one stage into the next stage.

Preferably the rotating components of each stage are mounted on a shaft which is common to all stages, although separate shafts may be used if required.

Any type of vessel may be used provided it is large enough for the mixture of solid and liquid to remain in it for an average detention period sufficient for the extractive action in the stage to be reasonably complete. Any type of agitator may be used in the vessel.

Any type of pump or other suitable device may be used to transfer the agitated mixture of liquid and solid to the feed-in zone of the screw press. Preferably the agitation is achieved by a rotating spider or paddle mounted on the same shaft as the screw and the transfer of the agitated mixture is achieved by means of a scoop or scoops mountdid ed on the rotating spider or paddle so as to pick up from the body of liquid and elevate and deliver it into the drainage zone of the screw. The scoop or scoops perform a dual function insofar as, in addition to elevating and transferring the mixture, they can be arranged, by their capacity in relation to the speed of rotation of the shaft, to meter or control the rate of passage of materials through the extractor.

The invention will be better understood by reference to the following description when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a plan view of one form of the apparatus with the cover open;

FIG. 2 is a front view with the cover omitted;

FIG. 3 is an end view of the cover;

FIG. 4 is an end view of an agitator;

FIG. 5' is a side elevation showing the sealing or choking means at the end of the screw; and

FIG. 6 is a diagrammatic sectional elevation of a screw press incorporating filter means for eliminating fines from the extraction liquor.

The embodiment of the invention shown in FIGS. 1 to 5 is particularly applicable to extraction with a volatile solvent in that the extraction is carried out in a sealed vessel. The vessel is supported on a suitable frame and is divided into a number of separate compartments 11 each of which forms the container for one stage. The vessel is provided with a hinged cover 12 provided with a gasket 13 on its periphery and is held closed by toggles 14. A shaft 15 passes through the vessel and has an agitator 16 mounted thereon for each of the containers 11. The agitator comprises a plurality of arms on one of which is mounted a scoop 17 A spiral screw is mounted on the shaft and is positioned inside a casing 19 the underside of which is perforated. A hopper 2% is fitted to the casing at the inlet end of the screw and the scoop 17 is so positioned that it will pick up material as it passes through the container and discharge it into the hopper when it reaches the upper portion of its path. The outlet end of the screw discharges into the container of the next stage and is fitted with a sealing or choking device. The sealing or choking device comprises an annular member 21 fitted around the shaft and carried on one end of an arm 22 the other end of which is pivotally mounted on a post 23 projecting upwardly from the casing. Springs 24 are connected to the arm to urge the annular member to the closed position. A collecting tray or platform 24a is fitted below each of the screw casings. The collecting tray of the second, third and fourth stages is connected to the container of the first, second and third stages respectively through pipes Each collecting tray is fitted with an overflow discharging into the container of the same stage. The collecting tray of the first stage is fitted with an outlet pipe 26. Raw material to be treated is fed to the container of the first stage through pipe 27 and solvent is fed to the container of the last stage through pipe 28.

The material to be treated is agitated in the container of each stage and as the scoop rotates, a small quantity of the material and solvent is picked up and discharged into the hopper 29. The solvent is squeezed from the material as it passes through the screw press and collects in the collecting tray from where it is passed to the preceding stage or returned through the overflow to the container or discharged through the outlet pipe 26. The material moves progressively through each stage and is finally discharged from the fourth stage into a de-solventiser (not shown) or into storage containers.

In order to avoid damage due to possible explosions, the cover is fitted with explosion doors. These comprise plates 29 pivotally mounted for rotation about one edge and resting on a flange 3% around an opening in the cover. The plates are fitted with gaskets of suitable maabove shows the use of four stages, the number may be varied.

The number of stages of extraction best suited to a particular application may be found by practical trial and error operation or it can be reasonably predicted by laboratory tests or by theoretical treatment.

Theoretical treatment must assume equilibrium conditions in each stage and can be expressed in the following equation in which the ratio of residual solute in the material coming out of stage n to the amount of solute in the ingoing raw material is:

where n is the number oi stages and R is the ratio of expressed backfiow liquid to liquid carried forward in the solid material after pressing in each stage and is assumed constant in all stages.

For example, consider a four-stage extraction (12:4) and the ingoing raw material contains one-third solute, that is, 0.5 pound solute to one pound of solid material or 8 :05. Say the amount of expressed liquid or backfiow is 0.65 gallon per lb. of solid material and the amount of liquid remaining in the solid is 0.15 gallon per lb. Hence R:0.65 divided by 0.15, or 4.33

To calculate the concentration of solute in the outgoing liquor, it has to be allowed that 0.65 gallon of backfiow per lb. enters the first vessel from the second stage whilst 0.15 gallon per lb. passes forwardly out of the first stage with the squeezed material and no liquid enters with the raw material. Hence, net volume of outgoing liquor is 0.5 gallon per lb.

Hence 0.5 minus 0.00142, or 0.49858 lb. is dissolved in 0.5 gallon.

This is equivalent to 0.997 lb. per gallon.

Operation of the extractor with relatively very small amounts of counterfiow liquid in proportion to solid material being extracted is achieved by fitting apportioning devices as described later at each stage so that the expressed liquor is returned partly back into the vessel from out of which it came and is partly allowed to flow back into the previous vessel in series.

With very porous or spongy materials it may be found, as an example, that a quite hard squeezed material may contain 0.15 gallon of liquid per 1b. of solid (i.e. the squeezed material contains 60% liquid and 40% solid). On the other hand, again as an example, it may be found that a consistency suitable for good agitation and efiicient extraction in each vessel may be 0.80 gallon of liquid per lb. of solid. Say, again as an example, it is desired to carry out the extraction with an outgoing liquor as small as 0.30 gallon per lb. of solid. Then this can be achieved by squeezing so that 0.15 gallon per lb. remains in the solid and 0.65 gallon per 1b. is squeezed out and then apportioning this 0.65 gallon so that 0.20 gallon flows back into the vessel from which it came out and 0.45 gallon passes back into the previous stage.

Thus an amount of 0.45 gallon per lb. passes back stage by stage into the first stage, but, in the first stage an r a o e liquor against the cost of providing and operating more stages. It is claimed thatthe provision of apportioning devices is a distinct advantage insofar as it permits of an almost unlimited choice in this regard. The choice of the number of stages may be reasonably predicted by the previously mentioned formula. Again, using the example 0.45 gallon bacldlow, the value R becomes 0.45 divided by 0.l5, or 3.0, instead of the previously mentioned 4.33. In order to achieve the same extraction ratio as in the previously mentioned four stages, namely it follows that in which case, if 11:5, the ratio is and, if 11:6, the ratio is Hence, with a backflow of 0.45 gallon per lb. instead of 0.65 gallon per 1b., five stages would not quite achieve as good extraction but six stages would give a comparably better extraction. lf six stages are used, the residual solute would be 0%29 or 0.0007 lb. solute per lb. of solid material.

in order to calculate the concentration of solute in the outgoing liquor, we have to allow that, although 0.45 gallon per lb. comes as backfiow into the first stage, the outgoing liquid is only 0.30 gallon per lb.

Thus, an amount of 0.5 minus 0.0007, or 0.4993 lb. is dissolved in 0.30 gallon. This is equivalent to 1.664 lbs. per gallon.

It follows, of course, that in making a choice in regard to degree of extraction, volume of counterfiow liquid used and the number of stages, there will be an ultimate limit setting the minimum volume of liquid according to the amount of solute in the raw material and the maximum solubility of the solute in the liquid.

It should be noted that with porous, spongy materials such as animal and fish protein and many cellulosic materials of a fibrous nature, an amount of liquid of the order of 0.3 gallon per lb. would be insufficient to provide a mixture thin enough to even agitate and most kinds of extraction would be very difficult. The advantage of the apportioning devices allows of a very small amount of counterflow, at the same time allowing of a much larger ratio of liquid to solid in the extraction vessels so as to permit or" efiicient agitation and extraction.

Any type of apportioning device may be used. One simple form of apportioning device comprises a tank to receive the expressed liquor from the screw press and connected to the container of the extractor unit with which it is associated through an overflow and to the container of the preceding extractor unit through a conduit or pipe fitted with a control valve. The control valve is open to allow the desired quantity of liquor to flow to the preceding extractor unit whilst the remainder of the liquor is returned to the extractor with which the apportioning device is associated through the overflow.

Another type of apportioning device which may be used comprises a tank to receive the expressed liquor from the screw press and having a pair of outlet pipes each provided with a control valve. ()ne outlet pipe is connected to the container of the extractor unit with which the device is associated whilst t is other outlet pipe is connected to the container of the preceding extractor unit. By opening the control valves on each of the outlet pipes to the desired extent, the amount of liquor flowing backwardly to the preceding extractor unit can be readily regulated.

In a third form of apportioning device, the tank receiving the expressed liquor from the screw press also has two outlet pipes connected in the same manner as in the second form of apportioning device described above. The inlet ends of the outlet pipes are substantially bell-mouthed and each provided with a substantially frustoconical plug on the end of an operating rod passing through the tank. The rate of flow of liquor into the respective outlet pipes can be readily varied by withdrawing the plugs to the desired extent.

In any type of apportioning device used for the purposes of the present invention, means may be provided for keeping the liquor in the device agitated if more than one phase exists and/ or the liquor has a relatively high fines content. If the liquid used in the extractor is highly volatile or if the extraction is carried out at a temperature approaching the boiling point of the liquid, the apportioning device should be incorporated within the container of the unit or should be sealed to reduce loss of vapour to a minimum.

The size of each container and the volume of mixture maintined therein are arranged so as to provide an appropriate mean or average detention period in the vessel. For example, in the particular form of the extractor described above a detention period of five minutes in each container is found to be adequate for the extraction of bone and proteinaceous material with acetone, so that in the four-stage unit as shown in FIGS. 1 to 5 of the drawings, the material is in process for a total period of only twenty minutes. This small period in process has two advantages-*the one that the size of the container is small and thus not expensive in proportion to the rate of throughput, and the other that if heat is applied and the material is susceptible to heat damage, the small period in process reduces the heat damage to a minimum.

If due to incorrect operation or unusual conditions there is a build up of the agitated mixture of liquid and solid in any one stage of the extractor, it is desirable to provide means for allowing the excess to flow into the preceding unit. This can be done by means of an interconnecting pipe or overflow channel connecting each of the successive extraction vessels. The pipe or channel may be fitted with a suitable control valve or flow regulating device.

If desired, the units may be arranged so that the level of agitated liquid and solids in each container is progres sively higher than the preceding container so that if the level of liquid in any vessel becomes too high, the agitated mixture may overflow back into the previous vessel. This return of mixture will of course reduce the throughput of the extractor by an amount corresponding to the amount of material or mixture returned to the previous vessel and should be maintained at an absolute minimum.

In the operation of the extractor, the matter of fine solid material coming out in the outgoing extraction liquor may present a problem. Ordinarily, this would be filtered if the outgoing liquor has to be evaporated or distilled for the purpose of recovering the extracted component and/ or re-using the liquid. In some cases, the fine material may be reasonably removed by settlement and decantation.

In the particular application of the extractor described above such as when raw comminuted animal bones are extracted with acetone, the outgoing iquor consists of a mixture of acetone and water and dissolved minor components and free fatty acids in one phase, melted neutral fat or oil in a separate liquid phase and the fine solid material is of a proteinaceous and bone nature. Settlement was found to be unsatisfactory insofar as the fat may rise to the top or sink to the bottom depending upon the specific gravity of the fat in relation to the specific gravity of the acetone-water phase and that the fat has a peculiar afiinity for the fine material and has a strong tendency to occlude or entrap it. Filtration without pressure was ineffective, whilst suction filtration failed due to the chilling action caused by the evaporation of some of the acetone resulting in congealing of the fat and blockage of the filter medium. Pressure filtration was found to be effective insofar as a clear mixed-phase liquor could be obtained but, then, the handling of the filter cake of fine material still presented a problem. it is necessary to recover the acetone from the cake without serious loss and, because the fine protein and bone material in the cake is not sufficiently extracted, it may require separate, further extractive treatment in order to recover it as acceptable reated product. Also, it is desirable that any handling of the outgoing liquor to separate and recover the fine material should be on a continuous and automatic basis and that the mixed liquid phases should be under agitation during the operation.

This problem may be overcome by arranging for the first stage screw press of the extractor to perform a filtering function so that the outgoing liquor is thus freed from fine material and hence no separate or ancillary filter is required in conjunction with the extractor. If the raw material being extracted is of overall relatively large particle size and contains only a small proportion of fine material, then it is found that the fine material coming back with the liquor stage by stage is substantially retrapped and carried forward stage by stage with the solid. in this case, a filtering function is needed only in the first stage. However, if the raw solid material is substantially all fine and contains insulficient larger particles to cause the re-trapping action, then it is desirable to arrange that all the stages incorporate a filtering function in the screw presses.

The filtering function is achieved by incorporating in the shell of the screw a filter medium instead of perforations or slots. In this case, the drainage zone may not be effective without pressure and the fed-in mixture of liquid and solid material may require to be under hydraulic pressure to assist the flow of liquid through the filter medium. This aspect of the invention is shown in FIG. 6 of the drawings.

Referring now to FIG. 6 of the drawings, the outlet end of the screw press er projects through the wall 62 of the container in which a body of liq id and solid material is contained. The portion of the shaft as at the inlet end of the screw press is equipped with a suitable enclosed shell 6d into which the material is fed under hydraulic pressure by a conventional pump. The pump may draw the material from a separate agitated tank or from the container of the extractor in which the unit is mounted or from a feed hopper into which the material is deposited by means such as the scoops shown in FIG. 1. The screw press is suitably designed to provide near the feed end an adequate area of filter medium 65 in its surrounding shell so that liquid is forced through the filter by the hydraulic pressure, whilst, at the same time, the rotation of the screw over the surface of the filter continually disturbs the filtered cake, thus preventing blockage of the filter and also propelling the filtered and thickened cake material forwards. At a fu'ther point, say, for example, half-way between the inlet and outlet ends of the screw, the design of the screw allows of a pressing action such as by a gradual expansion of the diameter of the shaft of the screw so that the material passing forwards is slowly forced into a smaller volume and further liquid is squeezed out through the filter medium 65 in the surrounding shell. A spring-loaded closure device 66 fitted at the outlet end of the screw press ensures that the flights of the screw towards the outlet end are kept full of compacted material and thus provide a resistance to any direct through flow of thinner mixture of liquid and solid from the inlet end under hydraulic pressure. When the unit is in settled down operation, the firmness of the compacted material in the flights should normally provide sufiicient resistance but the closure device is especially necessary at the start of operation to prevent the thin mixture from being forced directly through the spiral space along the screw.

The liquid expressed through the filter medium 65 drains into a surrounding hopper 67 the outlet of which may be fitted with a vflve es and which is provided with a steam inlet 69. Preferably the hopper and the filter medium are readily removable for cleaning and mainteuance.

Any suitable type of filtering medium may be used provided it conforms substantially to the shape of the screw so that the flights move over its surface or near its surface aud that it is strong enough to withstand the pressure exerted on it. It is also desirable that the filter medium be made of a material which is resistant to chemicals which may be used in dissolving out, from time to time, any accumulation of the fine material. For example, if the fine material is protein and bone and the liquor includes fat, then a suitable material would be a porous stainless steel which could be treated with caustic soda to dissolve protein and fat followed by dilute hydrochloric acid to dissolve any bone material clogging the filter.

Should the filtering medium become blocked, it can be readily cleaned by closing the valve 63 and blowing steam into the hopper through the inlet 6 The backward movement of steam through the filtering medium helps to clean same and at the same time may serve to bring the apparatus up to the operating temperature. If the filtering medium cannot be cleaned by back bio-wing with steam, it may be removed and unclogged by treatment with caustic soda and/or dilute hydrochloric acid or any other suitable compounds.

The closure device 66 may be used by itself 101 in creasing the pressure on the material as it nears the outlet end of the screw press, the diameter of the shaft remaining substantially constant throughout the length of the screw press. Other means for increasing the pressure on the material as it nears the outlet end or" the screw press comprise reducing the diameter of the press towards the outlet end or increasing the pitch of the flights of the screw towards the outlet end. The various means for increasing the pressure on the material as it moves towards the outlet end of the screw press may be used either singly or in combination. To facilitate the separation of the liquid from the material, if the liquid being used is not too volatile at the particular operating ten perature, the hopper receiving the liquid from the screen or filtering medium may be subjected to reduced pressure. Also, the screen or filtering medium may be positioned in any suitable position in the screw press casing.

The extractor of the present invention has general application in the dissolution of a soluble component or solute from a non-soluble component or solid, the liquid beiru water or any other desired liquid. It may also be applied to counter-current washing operations. It will achieve a maximum extraction or washing with the minimum usage of liquid, the outgoing liquor being heavily laden with the extracted component. It has particular application when the solid material being extracted is of a porous or spongy nature and has a strong tendency to cclude the liquid being used in the extraction. Furthermore, the extractor may be applied to porous or spongy materials when the component being extracted is not a true solute but is a fat or oil extracted by the liquid in a separate phase or in globule form or as an emulsion. The extractor is generally advantageous in applications where the outgoing liquor is very thick or viscous.

The extractor has other advantageous features in the nature of its mechanical simplicity and compactness which allow of cheapness of construction and also ease of sealing the extraction process if valuable and/ or inflammable solvents are being used. in this regard the press of th 8 last stage fulfills an additional function by providing a self-sealing core or plug of squeezed solid material at the point of egress from the extractor.

If desired, the extractor may be operated to provide an outgoing extraction liquor substantially or entirely free from fine solid material. Subject to appropriate sealing with or without heating, the extractor may be operated at pressures above atmospheric and at temperatures above the normal boiling point of the solvent or liquid used.

The extractor may be constructed in any range of sizes to allow for operations on a relatively small scale or on a very big scale. The screw presses used in the present invention do not require very heavy pressures to achieve their object as they do not solely determine the etficiency or economics of the over-all extraction process. Quite modest pressures of the order of 6 lbs. per square inch may be sufi'icient to express the liquid from the material being treated, and the required over-all efliciency is at tained by suitably arranging the backflow ratio and the number of stages.

I claim:

1. A continuously working counter-current extraction machine comprising a number of series connected stages, at least one of the stages comprising a vessel for a mixture of solid particulate material and a liquid, an agitator for agitating the mixture within the vessel, and a screw separating device for separating the solid particulate material from the liquid, delivering the separated solid to the vessel of the next-forward stage and discharging the separated liquid into the vessel of the next-backward stage, the agitator and the screw separating device rotating on a common shaft and the agitator carrying at least one scoop which delivers a quantity of the solid particulate material and liquid mixture to the feed end of the screw separating device.

2. A continuously working counter-current extraction machine as claimed in claim 1 wherein the solid outlet of the screw separating device has a resilient closure with a restraining spring.

3. A continuously working counter-current extraction machine comprising a number of series connected stages, a majority of the stages each comprising a vessel for a mixture of solid particulate material and a liquid, an agitator for agitating the mixture within the vessel, and a screw separating device for separating the solid particulate material from the liquid, delivering the separated solid to the vessel of the next-forward stage and discharging the separated liquid into the vessel of the nextbackward stage, the agitator and screw separating device of each stage rotating on a substantially horizontal shaft common to all stages and the agitator of each stage carrying at least one scoop which delivers a quantity of the solid particulate material and liquid mixture to the feed end of the screw separating device in the same stage.

4. A continuously working counter-current extraction machine as claimed in claim 3 wherein the solid outlet of the screw separating device of at least one of the stages has a resilient closure with a restraining spring.

References (Iited in the file of this patent UNITED STATES PATENTS 1,834,577 Cline Dec. 1, 1931 2,012,298 Berge Aug. 27, 1935 2,098,110 Schertz et al. Nov. 2, 1937 2,293,666 Bonotto June 11, 1940 2,390,388 Rector Dec. 4, 1945 2,547,577 Hamacher et al. Apr. 3, 1951 

1. A CONTINUOUSLY WORKING COUNTER-CURRENT EXTRACTION MACHINE COMPRISING A NUMBER OF SERIES-CONNECTED STAGES, AT LEAST ONE OF THE STAGES COMPRISING A VESSEL FOR A MIXTURE OF SOLID PARTICULATE MATERIAL AND A LIQUID, AN AGITATOR FOR AGITATING THE MIXTURE WITHIN THE VESSEL, AND A SCREW SEPARATING DEVICE FOR SEPARATING THE SOLID PARTICULATE MATERIAL FROM THE LIQUID, DELIVERING THE SEPARATED SOLID TO THE VESSEL OF THE NEXT-FORWARD STAGE AND DISCHARGING THE SEPARATED LIQUID INTO THE VESSEL OF THE NEXT-BACKWARD STAGE, THE AGITATOR AND THE SCREW SEPARATING DEVICE ROTATING ON A COMMON SHAFT AND THE AGITATOR CARRYING AT LEAT ONE SCOOP WHICH DELIVERS A QUANTITY OF THE SOLID PARTICULATE MATERIAL AND LIQUID MIXTURE TO THE FEED END OF THE SCREW SEPARATING DEVICE. 